PORTLAND, Maine — Two species of bats that have been devastated by the deadly white nose syndrome are among the animals state officials propose to reclassify as endangered. State wildlife officials also propose classifying a third bat species as threatened.

Joining the bats are two species of birds — the black-crowned night heron and the great cormorant — as well as a beetle, butterfly and land snail.

A species of mayfly and butterfly also are being proposed for an upgrade from endangered to the less severe designation of “threatened” as part of a slate of animal classification changes under public review.

The state Department of Inland Fisheries and Wildlife held a hearing on the changes Monday night in Portland, with a second hearing scheduled to take place Tuesday night in Farmington.

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For the bats, whose plight in the northeastern United States has been well publicized, one Maine environmentalist said the new listings “may be too late.”

The little brown and northern long-eared species of bats are being proposed for endangered classifications, while the eastern small-footed bat is in line to be called threatened.

“They spend the summers in different places, but in the winters, they all get together and hibernate together, so they’re more susceptible to white nose syndrome. They get it from each other,” said Susan Gallo, a wildlife biologist for the Falmouth-based Maine Audubon Society. “They’ve totally crashed. We don’t have huge bat populations in Maine, but … we’ve had places where we’d seen 200 to 300 to 600 bats now down to just a dozen. In some places, those northern long ears are gone. In some places, they’re not showing up at all.”

Gallo said that state wildlife officials consider a variety of criteria when deciding whether to list a vertebrate species as endangered, but one is when its population drops below 500 total individuals or 200 breeding individuals.

For invertebrates, those population thresholds are 1,000 total individuals or 500 breeding individuals.

“The one index we can be certain of is when the bats aggregate in winter,” said Charlie Todd of the Maine Department of Inland Fisheries and Wildlife. “We’ve been monitoring those [winter populations] over time, and we’ve seen a 90 percent decline in their population. … Our winter counts have gone from the hundreds to the tens, but we really can’t speculate on the summer populations.”

The white nose syndrome is a fungal infection harmless to humans, but it thrives in cave-like environments and decimates bats where they hibernate.

Such infections are not what’s plaguing the birds being proposed for the endangered species list, Todd said.

The rebound of Maine’s eagle population has taken a toll on the state’s great cormorant, Todd said, as eagles prey upon cormorants. That, combined with suspected declines in quality and quantity of the fish cormorants and herons eat, have driven down populations of the coastal birds.

“Both birds have two kinds of vulnerability: Low numbers, and they like to gather colonially,” he said.

When large populations of any animal gather in few locations, their species is left more susceptible to environmental dangers in those areas — “it’s like having all your eggs in one basket,” Todd said.

Todd said Maine’s great cormorant population has declined to five colonies with a total of about 50 breeding pairs, down from 264 breeding pairs in 1992. He said the black-crowned night herons are similarly down to about 50 breeding pairs in just four island locations, almost half of the 95 breeding pairs seen at seven locations in 2006.

Todd said the invertebrates being proposed for endangered classifications are even more isolated. The six-whorl vertigo land snail still numbers in the thousands, but it can only be found near the less acidic limestone and bedrock conditions of eastern Aroostook County.

The cobblestone tiger beetle and frigga fritillary butterfly species are both down to the hundreds in population, and they can only be found in Somerset and northern Piscataquis counties, respectively, Todd said.

“Placing them on the endangered list doesn’t imply that we have the solution for saving them, but it does marshall more conservation resources to help educate the public about them and maybe help turn things around for them,” he said.

The roaring brook mayfly and the Clayton’s copper butterfly are being proposed for upgrades from endangered to threatened.

“They’re moving in the right direction,” Todd said. “We’ve found more occurrences, and there’s more stability to their habitats than we thought there was in the past.”

Individuals can submit written comments about the classification changes by Aug. 15 to Becky Orff, Inland Fisheries and Wildlife, 284 State St., 41 State House Station, Augusta, Maine, 04333, or email becky.orff@maine.gov.